I am not an expert. My understanding - (1) The quantity of rocks that would be needed to explain such a gigantic gap in mass is bound to be observed - if they

I am not an expert. My understanding - (1) The quantity of rocks that would be needed to explain such a gigantic gap in mass is bound to be observed - if they are dark, then at least we should be able to see them when they block light. You have to remember we need dark matter to be around 80% of total mass of the universe. So they either need to be super dense, like tiny black holes [1], or there needs to be so much of it that there is no way we won't see them. (2) Dark matter is too spread out. If they were rocks or any of the known matter types, they should have coalesced on their own. So they have to be such that dark matter doesn't interact with itself. Edit: This is a nice intro: https://www.youtube.com/watch?v=fidzLZQyaJE https://www.youtube.com/watch?v=fidzLZQyaJE Edit 2: Also worth pointing out that dark matter is not the only explanation: https://www.youtube.com/watch?v=4_qJptwikRc https://www.youtube.com/watch?v=4_qJptwikRc [1] https://duckduckgo.com/?q=can+dark+matter+be+tiny+black+holes&atb=v188-1&ia=web&iai=r1-0&page=1&sexp=%7B%22biaexp%22%3A%22b%22%2C%22msvrtexp%22%3A%22b%22%7D https://duckduckgo.com/?q=can+dark+matter+be+tiny+black+hole...